How to Adjust the ZPD DLink Phase
The BaBar DAQ system is a bit picky about the phase of the dlink data.
Simply clocking with the dclk isn't enough, since the ZPD does this internal
to the Decoder/Driver FPGA which produces different delays than the BLT
which uses an external chip. The ZPD firmware must adjust the dclk phase
to hit the magic sweet spot that matches the BLT. Here's how to do that:
The dclk phase is adjusted in
fastcontrol/clk_input
which is included on the top level diagram of
zpd/decoderdriver.
The relevant part is:
attribute phase_shift of dclk_dcm : label is -30;
That phase runs -128 to 127. When the sweet spot is found, it should be
entered here.
When searching for the sweet spot, it is a hassle to have to go through
the entire generation/synthesis/implementation cycle to test a new value.
Here's how you can try a new value by editing the post-implementation
Xilinx files:
-
In the Xilinx Project Navigator, open a Decoder/Driver project
and implement it if you haven't already done so.
-
Double click on "View/Edit Routed Design (FPGA Editor)"
-
On the right is a button called "editmode". Click this until "Read Write"
appears in the status bar in the lower right hand corner of the main window.
-
In the "List1" subwindow, change the Name Filter to *dcm* and click Apply.
-
Highlight the item with a name like "I21_dclk_dcm" and then click on the
"Zoom Selection" button
on the toolbar.
-
Double click the red highlighted DCM component. This will pop up a component
editor window.
-
Click the "begin editing" button
on the toolbar.
-
Click the Show/Hide Attributes button
on the toolbar
-
Change the PHASE_SHIFT to a new value.
-
Click the Apply toolbar button
and close the component editor window.
-
Click the Save toolbar button
of the main window.
-
Exit the FPGA Editor.
-
Back in the Xilinx Project Navigator,
generate the programming file and then use
iMPACT to create the ACE file, etc.
That may seem like a lot of steps, but it is a lot fewer than if you had
to start from a change in the VHDL source code.
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